This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-040663, filed Feb. 16, 2001, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical fiber and an optical transmission line used suitably in a wavelength division multiplexing (WDM) optical communications.
2. Description of the Related Art
As a technique for increasing the transmission capacity in the optical transmission using optical fibers, the WDM (wavelength division multiplexing) optical transmission has become a focus of attention recently, and many intensive studies have been conducted on optical fibers which are employed suitable in the WDM optical transmission.
Incidentally, well-known examples of the optical fiber which can be used for the WDM optical transmission are a single mode optical fiber (SMF) having a zero dispersion near a wavelength of 1.3 xcexcm and a dispersion shift type optical fiber which does not have a zero dispersion in a wavelength band in use (NZDSF); however these types of optical fibers have a problem of non-linearity. Under these circumferences, there is a demand of developing a new type of optical fiber.
More specifically, in order to solve the problem of non-linearity, an optical fiber has been developed, in which the dispersion value is set fully away from zero and the effective core area Aeff is enlarged. Examples of such an optical fiber is discussed in Collection of Lecture Notes C-3-76 and C-3-77 for the Electronics Society Convention 1999 held by the Institute of Electronics, Information and Communication Engineers.
However, those types of optical fibers discussed in Lecture Notes C-3-76 and C-3-77, each exhibits a dispersion value of more than 20 ps/nm/km, and therefore the cumulative amount of dispersions of fibers when an optical transmission line is formed of these fibers, increases. With such an increased amount of dispersion, the transmission line cannot be appropriately used for a long-distance WDM optical transmission.
An object of the present invention is to provide an optical fiber which has a dispersion value maintained at a similar level to that of the conventional SMF and is more suitable for the WDM optical transmission than the conventional SMF.
Another object of the present invention is to provide an optical transmission line comprising the above-described optical fiber, which is suitable for the WDM optical transmission.
According to an embodiment of the present invention, there is provided an optical fiber comprising a center core portion, a side core portion and a clad portion in an order from an inner side, which has a dispersion value of 14 ps/nm/km or higher and 20 ps/nm/km or less at a wavelength of 1550 nm, a dispersion slope of 0.05 ps/nm2/km or higher and 0.08 ps/nm2/km or less at a wavelength of 1550 nm and a transmission attenuation of 0.2 dB/km or less at a wavelength of 1550 nm, wherein a relative refractive index difference xcex941 between the center core portion and the clad portion is 0.25% or larger and 0.50% or less, a relative refractive index difference xcex942 between the side core portion and the clad portion is 0.05% or larger and 0.30% or less, an inequality xcex942 less than xcex941 is satisfied, a ratio a/b between an outer diameter a of the center core portion and an outer diameter b of the side core portion is 0.3 or higher and 0.7 or less, and an effective core area Aeff at a wavelength of 1550 nm is 90 xcexcm2 or larger.
According to another embodiment of the present invention, there is provided an optical transmission line comprising a plurality of optical fibers, configured to transmit optical signals, wherein at least one of the plurality of optical fibers is the above-described optical fiber.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be leaned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.